1. Field of the Invention
The invention relates to a magnetic trip device for a circuit breaker and, more particularly, to a support structure for a moveable core of the magnetic trip device. The invention also relates to a circuit breaker including a magnetic trip device and a support structure for a moveable core of the magnetic trip device.
2. Background Information
Molded case circuit breakers are well known in the art. Examples are disclosed in U.S. Pat. Nos. 4,503,408; 5,927,484; and 6,366,187, which are incorporated by reference herein.
Molded case circuit breakers typically include separable contacts, an operating mechanism, and a trip unit, which are mounted inside of a molded plastic insulative housing.
A common type of magnetic trip device for a trip unit is a solenoid, which includes a stationary core through which passes the current in the protected circuit. This current creates a magnetic field. When there are very high instantaneous currents, such as those associated with a short circuit, the magnetic field intensifies. The magnetic trip device may include a plunger assembly having a moveable core and a plunger tab, which engages a trip latch on the operating mechanism. The plunger assembly is partially disposed within the stationary core. Typically, a spring provides a limited force biasing the moveable core away from the stationary core and preventing the plunger from engaging the trip latch. When a short circuit occurs, the current in the stationary core creates a magnetic field strong enough to overcome the moveable core spring, thereby allowing the moveable core to move toward the stationary core and causing the plunger to engage the trip latch.
Adjusting the amount of separation between the plunger assembly and stationary core may control the amount of current required to trip the circuit breaker. When the plunger assembly is located closer to the stationary core, a weaker magnetic field, and therefore a lower current, is required to draw the plunger assembly toward the stationary core. In order to adjust the trip condition, the plunger assembly is mounted in a plunger assembly support structure having a base and a moveable plunger carriage. The carriage allows the plunger assembly, including the moveable core, to be moved relative to the stationary core. A carriage is employed, in order that adjusting the gap between the moveable core and the stationary core does not impact on the compression of the moveable core biasing spring. The moveable plunger carriage is coupled to an adjustment mechanism to address the initial gap between the plunger assembly and the stationary core.
U.S. Pat. No. 6,366,187 discloses a plunger assembly support structure, which maintains the orientation of a plunger carriage in the circuit breaker housing, maintains the moveable core alignment with the stationery core, and corrects rotation of the plunger tab on the moveable core. During operation of the trip mechanism, it is possible for the moveable core to rotate axially, thereby allowing the plunger tab to move out of alignment with the actuating arm of the trip bar. The plunger tab contacts a plunger guide. As the plunger carriage travels from a first position towards a second position, the plunger tab contacts a conical indentation and rotates the moveable core, in order that the plunger tab is aligned with the trip bar actuating arm.
The moveable core of U.S. Pat. No. 6,366,187 rests in a slot of the plunger carriage. It is known to employ a conventional flat washer having an opening about the moveable core and positioned between the plunger carriage slot and a plunger assembly spring. In the event of an over-current condition, the moveable core may move within the slot and, hence, the position of the moveable core in the plunger carriage may change. This causes the plunger tab to hit random locations of the trip bar actuating arm. As a result, the trip current level is inconsistent.
Accordingly, there is room for improvement in circuit breakers and magnetic trip devices having a moveable core support structure.
These needs and others are met by the present invention, which provides a positioning member having a hook and an opening. The hook engages the wall of a plunger assembly support structure. A moveable core passes through the opening of the positioning member, which retains the moveable core relative to the plunger assembly support structure.
As one aspect of the invention, a circuit breaker comprises: a housing; at least one pair of separable contacts disposed in the housing; a latchable operating mechanism structured to separate the at least one pair of separable contacts; a magnetic trip mechanism coupled to the latchable operating mechanism, the magnetic trip mechanism including a plunger assembly support structure and a plunger assembly having a moveable core, the plunger assembly support structure including a wall having a slot therein, the moveable core resting in the slot; and a positioning member having a hook and an opening, the hook engaging the wall of the plunger assembly support structure, the moveable core passing through the opening of the positioning member, which retains the moveable core relative to the plunger assembly support structure.
The plunger assembly support structure may include a plunger carriage assembly having a member, which engages the hook of the positioning member.
The positioning member may position the moveable core at a fixed distance from the plunger assembly support structure.
As another aspect of the invention, a plunger assembly support structure for a plunger assembly of a magnetic trip mechanism comprises: a base including a wall having a slot therein; a plunger assembly having a moveable core resting in the slot; and a positioning member having a hook and an opening, the hook engaging the wall of the base, the moveable core passing through the opening of the positioning member, which retains the moveable core relative to the base.
As another aspect of the invention, a positioning member comprises: a washer portion having an opening; and a hook portion disposed from the washer portion.
The hook portion may be a J-shaped hook portion.